1. Field of the Invention
The present invention relates to an image processing apparatus and method, and more particularly to an image processing for using an image memory area efficiently.
2. Description of Related Art
Recently, with the cost reduction of memories and hard disks and the performance enhancement of CPUs, apparatuses have been spread which can carry out a plurality of functions simultaneously with a single image input/output unit. In addition, with the spread of computers and networks, connecting a network interface to the image input/output unit enables the transmission and reception of image data through the networks. Specifically, copying machines have been proposed which read a document with an optical reader, store image data passing through analog-to-digital conversion in a hard disk, and then send the image data stored in the hard disk to a destination a user designates by fax, or carry out copying or printing the user designates. In addition, copying machines can have a network interface, in which case functions such as sending the stored image data to a designated computer via a network can be installed. In contrast, such functions can be installed as generating and outputting image data according to a printer description language that is output from a computer.
As image data the copying machines handle, there are a lot of examples such as documents read by optical readers of the copying machines and image data based on the printer description languages fed from the computers. Recently, however, since users can produce color data easily because of the cost reduction and performance improvement of the computers, the image data handled by the copying machine are shifting from the black-and-white image data to color image data.
Generally, the color image data have a data quantity twice or more than that of the black-and-white image data. Accordingly, when the copying machine handles the color image data, the data quantity greatly increases. Thus, the image data are stored in a memory with being subjected to irreversible compression, and the processing at the transmission to the computer via the network or at printing is carried out through the expansion of the compressed image data. In addition, to perform optimum image processing at the color image printing, image processing adjustment at the printing is performed by deciding image area information about colors and characters on each page of the color image data (for example, see Japanese patent application laid-open No. 2000-305744).
As for these processings, a designation of the user enables a plurality of processings to be carried out collectively. More specifically, the image data read by the optical reader of the copying machine are stored in the hard disk and are transmitted to computers on the network, followed by a print instruction of the image data stored in the hard disk by the user. This makes it possible to print the irreversible compressed image data in the hard disk by expanding the image data. Normally, the data stored in this case are only one kind of the irreversible compressed image data. Thus, to perform transmission or printing, the irreversible compressed image data must undergo color space conversions or image format conversions at the expansion according to the uses. This is because to generate and store the image data for each of the individual uses, a plurality of image data must be generated for the individual uses. This will result in the consumption of a large amount of image memory for each user designation, which can bring about interruptions of the processings of other users.
Although the irreversible compression of the color image as described above can reduce the image capacity of the color image data, the expansion offers a problem of deteriorating the image quality as compared with the original image data. To print such image data, screen processing is performed on the image data at the printing, which makes the deterioration of the image quality inconspicuous. However, to send the image data to a computer or by FAX via the network or public telephone circuit as digital data, the data that are not subjected to the screen processing are sent. Accordingly, when looking at the image on a receiving side unit, the degradation in the image quality becomes conspicuous. In particular, in JPEG generally used as the irreversible compression of color images, since the processing is carried out on a block by block basis in the compression process, block noise is easy to take place.
On the other hand, to suppress such degradation in the image quality, reducing the compression rate at the irreversible compression is effective. This, however, has a problem of increasing the memory capacity after the compression.
The present invention is implemented to solve the foregoing problems. It is therefore an object of the present invention to provide an image processing apparatus and method capable of using the image memory area efficiently in accordance with the processing content the user sets.